Ethylene glycol (EG) is an important and widely used raw material in organic chemical industries. Ethylene glycol is mainly used for producing polyacetate fibers, antifreezing agents, unsaturated polyester resins, lubricants, plasticizers, non-ionic surfactants and explosives. Furthermore, ethylene glycol also can be used in many fields including paint, photographic developer, brake fluid, ink and the like, used as a solvent and medium for ammonium perborate, and used for producing special solvents such as glycol ether.
At present, China has surpassed the United States to become the largest ethylene glycol consumer in the world. The average annual growth rate of apparent domestic ethylene glycol consumption from 2001 to 2006 is 17.4%. Although China's ethylene glycol production capacity and output are growing rapidly, the increasing market demand still cannot be satisfied due to the strong development of related industries such as the polyester industry. A large number of ethylene glycol has to be imported every year and its import quantity is increasing year by year.
Currently, large domestic and foreign ethylene glycol producers adopt a direct hydration of ethylene oxide, i.e. the pressured hydration process, for the commercial production of ethylene glycol. This production process is only grasped by three companies, Royal Dutch/Shell Group, Halcon-SD, U.S.A. and UCC, U.S.A. In addition, the research and development of new synthesis processes of ethylene glycol are still progressing. By way of example, Shell, UCC, Moscow Mendeleev Institute of Chemical Process, Shanghai Petrochemical Institute and others have developed an ethylene glycol production process involving the catalytic hydration ethylene oxide; Halcon-SD, UCC, Dow Chemical, Japan Catalysis Chemical, Mitsubishi Chemical and others have developed a process for producing ethylene glycol from ethylene carbonate; and Dow Chemical and others have developed a process for producing ethylene glycol via a coproduction of EG and dimethyl carbonate (DMC).
As for the direct hydration method, due to the high water content of the reaction product, the subsequent equipment (i.e. evaporator) needs an extended processing procedure, a large size and a high energy consumption and the total yield of the process is only about 70%, which has directly impacted the cost for the production of ethylene glycol. In comparison with the direct hydration method, the catalytic hydration method can greatly reduce the water content of the reaction product, and increase the conversion of the feedstock and the EG selectivity. If the catalyst stability problem and related engineering and technical problems could be solved successfully, the replacement of the non-catalytic hydration process with the catalytic hydration process in EG production would be irresistable. Ethylene carbonate (EC)-to-EG production process is superior over the EC direct hydration method in the conversion of feedstock, EG selectivity and the consumption of feedstock and energy, and thus is an advanced method. The EG and DMC coproduction process can make full use of the CO2 by-product of the ethylene oxidation process, so that two high valuable products can be produced in existing EC production plant by simply adding a reaction step for producing EC, which is very attractive.
However, the above-described methods share a common drawback of the consumption of ethylene, which is mainly derived from traditional petroleum refining at present. Since the high global petroleum price will be sustained for a long period in the future, the route for production of ethylene glycol from abundant and cheap natural gas or coal instead of petroleum (non-petroleum route, also known as CO route) becomes a competitive one for the traditional ethylene route. Among others, new techniques for the production of EG from syngas may have great influence on the innovation of EG production processes. A very attractive route in coal chemical industry for the production of EG is to produce dimethyl oxalate by using CO as a starting material and subsequently convert dimethyl oxalate into EG via hydrogenation. By far, the study at home and abroad on the production of dimethyl oxalate from CO has yielded good results, and a mature industrial production process has been developed. However, as for the hydrogenation of dimethyl oxalate to EG, there is still a lot of work to do in research. In particular, there is still no breakthrough in the study on how to effectively improve the selectivity to ethylene glycol and improve the stability of the catalyst.
It is disclosed in Spectroscopy Laboratory, 2010, 27 (2), pages 616-619, a hydrogenation catalyst useful for producing ethylene glycol from dimethyl oxalate, which is a Cu—B/γ-Al2O3 or Cu—B/SiO2 amorphous alloy catalyst prepared by chemical reduction deposition and the evaluation of which shows a low oxalate conversion and an EG selectivity of less than 90%.
It is disclosed in CN200710061390.3 a hydrogenation catalyst useful for the synthesis of ethylene glycol from an oxalate and the preparation thereof, with which the oxalate conversion achieved is relatively low, typically about 96%, and the EG selectivity achieved is about 92%.
The main problem present in the above documents lies in the low EG selectivity, which still needs to be enhanced and improved.